Starter motors

ABSTRACT

A starter motor for an internal combustion engine comprising an electric motor capable of rotating a shaft. A pinion gear wheel carried by the shaft, and rotatable therewith, the gear wheel also being movable axially relative to the shaft. An electromagnet including an armature which is coupled to the pinion gear wheel so that the two can move axially relative to the shaft. The electromagnet also includes a plurality of electromagnet poles which are equi-angularly spaced around the shaft in a plane at right angles to the axis of the shaft, and which are spaced apart by an amount such that the armature can enter between the poles. In the rest position of the armature there is a clearance between the poles and the armature in the direction of movement of the armature. The shaping of each pole is such that the surface of the pole presented to the armature includes regions which are spaced from the armature by different distances in the direction of movement of the armature, and which are equally spaced from the shaft in a radial direction. The electromagnet further includes a member which magnetically interconnects the poles and a winding associated with the poles so that when energised there is a flow of magnetic flux between the poles and the armature, within the armature at right angles to the direction of movement thereof, and between the poles by way of said member, such that the armature is attracted to the poles. The arrangement of said regions of the pole surfaces is chosen to achieve a predetermined attraction between the poles and the armature during the movement of the armature towards the poles.

United States Patent [1 1 .Wilson 1 Nov. 12, 1974 STARTER MOTORS [75]Inventor: Ronald Wilson, Birmingham,

England [73] Assignee: The Lucas Electrical Company Limited, Birmingham,England [22] Filed: Nov. 7, 1973 [21] Appl. No.2 413,455

[30] Foreign Application Priority Data Nov. 10, 1972 Great Britain51994/72 [52] U.S. Cl. 310/209, 123/179 M, 290/38 A, 310/216 [51] Int.Cl H02k 1/06, F02n 1l/02 [58] Field of Search 310/79, 17, 80, 216, 179,310/193, 258, 209, 191; 290/38 A, 48;

Primary Examiner-J. D. Miller Assistant Examiner-Robert .l. HickeyAttorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A starter motorfor an internal combustion engine comprising an electric motor capableof rotating a shaft. A pinion gear wheel carried by the shaft, androtatable therewith, the gear wheel also being movable axially relativeto the shaft. An electromagnet including an armature which is coupled tothe pinion gear wheel so that the two can move axially relative to theshaftLThe electromagnct also includes a plurality of electromagnet poleswhich are equi-angularly spaced around the shaft in a plane at rightangles to the axis of the shaft, and which are spaced apart by an amountsuch that the armaturecan enter between the poles. in the rest positionof the armature there is a clearance between the poles and the armaturein the direction of movement of the armature. The shaping of each poleis such that the surface of the pole presented to the armature includesregions which are spaced from the armature by different distances in thedirection of movement of the armature, and which are equally spaced fromthe shaft in a radial direction. The electromagnet further includes amember which magnetically interconnects the poles and a windingassociated with the poles so that when energised there is a flow ofmagnetic flux between the poles and the armature, within the armature atright angles to the direction of movement thereof, and between the polesby way of said member, such that the armature is attracted to the poles.The arrangement of said regions of the pole surfaces is chosen toachieve a predetermined attraction between the poles and the armatureduring the movement of the armature towards the poles.

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PATENTEL M 1 21914 3,848,148

SHEET 3 OF 3 FULL -05 '10 45 2O 25 3O '55 INCHES ARMATURE. & PINIONMOVEMENT STARTER MOTORS This invention relates to starter motors forinternal combustion engines.

A starter motor according to the invention comprises, an electric motor,a shaft rotatable by said motor and carrying a pinion gear wheel, thepinion gear wheel being rotatable with said shaft and being movableaxially relative to the shaft between a rest position and an operativeposition, and an electromagnet including an armature coupled to thepinion gear wheel said armature and said pinion gear wheel being movableaxially relative to said shaft, a plurality of electromagnet polesequi-angularly spaced around the axis of said shaft in a plane at rightangles to said axis and spaced apart by an amount such that the armaturecan enter between the poles, the poles being spaced from the armature,in the rest position thereof, in the direction of movement of thearmature relative to the shaft, each pole being shaped so that thesurface of each pole presented to the armature in the rest position ofthe armature includes regions spaced from the armature by differentdistances in the direction of movement of the armature, and equallyspaced from said shaft in a radial direction a member magneticallyinterconnecting the poles, and an electromagnet winding associated withthe poles so that when energised the winding induces a flow of magneticflux between the poles and the armature, within the armature at rightangles to its direction of movement, and between the poles, by way ofsaid member, so that the armature is attracted to the poles, thearrangement of said regions of the pole surfaces being chosen to achievea predetermined attraction between the poles and the armature during themovement of the armature towards the poles.

One example of the invention is illustrated in the accompanying drawingswherein:

FIG. 1 is a diagrammatic representation of a starter motor,

FIG. 2 is a front elevational view of one of the electromagnet polesshown diagrammatically in FIG. 1,

FIG. 3 is a sectional view on the line 3-3 in FIG. 2,

FIG. 4 is a plan view of the pole shoe of the pole shown in FIGS. 2 and3,

FIGS. 5 to 11 are plan views respectively of alternative forms of poleshoe for use with the pole body of the pole shown in FIG. 2 and,

FIG. 12 is a graph illustrating the effect of the pole shape shown inFIG. 5.

Referring to the drawings, the starter motor includes an electric motorindicated diagrammatically at 11 which rotates a shaft 12 supported inbearings (not shown) carried by the casing 13 of the starter motor.Carried by the shaft 12 is a pinion assembly 14 including a pinion gearwheel 15 and a roller clutch 16. The pinion assembly 14 is movableaxially relative to the shaft 12 between a rest position, and anoperative position in which the pinion gear wheel 15 engages, in use, aring gear of an engine to be started. The pinion assembly rotates withthe shaft 12, although in certain circumstances the pinion gear wheel 15can rotate relative to the shaft 12 as permitted by the roller clutch16. Normally however the pinion gear wheel 15 rotates with the shaft 12.Associated with the pinion assembly 14 is an electromagnet armature 17which is generally in the form of a thick steel disc slidably mounted ona sleeve 14a of the pinion assembly. A spring 18 urges the armature 17against an abutment 19 secured to the sleeve 14a.

The portion of the casing 13 encircling the shaft 12 adjacent the pinionassembly 14 is cylindrical, and is concentric with the shaft 12. Thisportion of the casing 13 is formed from mild steel, and asecured to theinner surface thereof are a pair of diametrically opposed electromagnetpoles 21, the poles 21 are magnetically interconnected by the casing 13and each pole includes a pole body 22 which extends radially inwardlyfrom the casing 13 towards the shaft 12 at its innermost end each polebody 22 is shaped to receive a pole shoe which defines part of thesurface of the pole which is presented to the armature 17, and alsodefines the radially innermost surface of the pole. The pole bodies 22and pole shoes are shaped so that their radially innermost surfaces,presented to the shaft 12, are cylindrical, the radially innermostsurfaces of the two poles defining parts of a common, imaginary cylinderhaving its axis coincident with the axis of the shaft 12 and of diametersuch that the armature can enter between the poles with a minimal airgap. The two pole bodies 22 are substantially identical, and in use eachwill receive a substantially identical pole shoe. Several forms of poleshoe are possible, and eight different pole shoe forms are shown inFIGS. 4 to 11, respectively. The pole shoe 23 shown in FIG. 4 issymmetrical and the surface of the pole shoe 23 which is presented tothe armature 17 in use is stepped at its opposite ends, in the directionof movement of the armature. Thus, in use the central land 23a of thefront surface of the pole shoe 23 will be closer to the armature thanthe remainder of the pole shoe 23 by virtue of the steps 23b. The poleshoe 24 shown in FIG. 5 is again symmetrical, and differs from the poleshoe 23 in that the single step 23b of the shoe 23 is replaced by doublesteps 24b, 24c. Thus the central land 24a will be closer to the armaturethan the stepped region 24b and the stepped region 24b will be closerthan the region 24a. The pole shoe 25 shown in FIG. 6 is notsymmetrical, since the steps provided in one end of the front surfaceare dimensioned differently to the steps provided in the other end ofthe front surface. FIGS. 7 and 8 show further asymmetric pole shoes 26,27 wherein only one end of the front surface is stepped. FIGS. 9 and 10show shoes 28 and 29 wherein the right angle steps are replaced bylinear tapering regions 28a, 29a and FIG. 11 shows a shoe 31, where theright angle steps are replaced by curved regions 31a. The regions of thepoles spaced by different distances from the armature are, as is clearfrom the drawings, equally spaced from the shaft 12 in the radialdirection.

Each of the pole shoes 23 to 31 is capable of being secured to the polebody 22, the pole body 22 having therein a pair of threaded bores whichreceive countersunk screws passing through countersunk holes in the poleshoes to retain the pole shoes on the pole body.

Encircling each of the poles 21 between the casing 13 and its respectivepole shoe is an electromagnet winding 20. The windings 20 can beelectrically interconnected in parallel or in series, and are soarranged that when current flows in the windings 20 the poles assumeopposite magnetic polarities. Thus magnetic flux will flow from one ofthe poles to the armature 17, will flow in the armature 17 at rightangles to the shaft 12, from the armature 17 back to the other of thepoles, and

from said other pole back to said one pole by way of the casing 13,thereby attracting the armature 17 towards the poles and moving thepinion assembly 14 axially relative to the shaft 12 from its restposition towards its operative position. The winding 20 will normally beenergised by way of a manually controlled switch which simultaneously,or after a short delay, also energises the motor 11. Alternatively, themotor 11 can be energised by closure of a further switch dependent uponmovement of the armature to a position corresponding to the operativeposition of the pinion 15.

The imaginary cylinder defined in part by the radially innermostsurfaces of the poles 21 is of slightly larger diameter than theexternal diameter of the disc-like armature 17. Thus the armature 17 canenter between the poles 21, and in the operative position of the pinionassembly 14 the armature 17 lies between the poles 21. The steppednature of the surfaces of the poles presented to the armature 17, withthe steps or curved surfaces running in the direction of movement of thearmature 17, modifies the electromagnetic force acting on the armature17 at various points in its movement between the rest position and theoperative position. Thus the different pole shoes will provide differentcharacteristics, and all of the pole shoes shown in the drawings aredesigned to modify in various ways the characteristics of the attractionwhich occurs between the armature and a pair of plain poles as thepinion assembly of the starter motor approaches its operative position.FIG. 12 shows in graph form a comparison between plain poles and polesof the form shown in FIG. 5. It can be seen that the plain polearrangement (curve 1) shows a substantial drop in pull between 0.15 and0.275 inches of pinion and armature movement. 0.00 represents the restposition and 0.35 represents the position wherein the pinion would be infull engagement with the toothed wheel of an engine to be started. Thepole form shown in FIG. 5, as can be seen from curve 2 of FIG. 12overcomes the drop in pull exhibited by the plain poles. Thecharacteristics produced by the other pole forms shown will differ fromthe characteristics illustrated in curve 2 and the pole form which ischosen for a particular starter motor will of course depend upon therequirements of the starter motor. For example, in a starter motor wheremovement of the armature to a position equivalent to full pinionengagement controls energisation of the motor field then it is importantthat the attraction of poles can overcome the spring 18 in the event oftooth to tooth abutment between the pinion and the engine ring gear. Insuch a case the pole form of FIG. might be chosen to ensurehighattraction at the point in the movement of the pinion assembly where thetooth to tooth condition would occur. Similarly the FIG. 5 pole formmight be chosen for a starter motor where the spring 18 is dispensedwith and there is no facility for relative movement between the armatureand the pinion assembly, the motor field being energised a shortpredetermined time after the winding 20 is .energised. In this case itwould be necessary'to have high attraction to move the pinion rapidlyinto full engagement before energisation of the motor field orimmediately a tooth to tooth condition has been relieved by rotation ofthe pinion upon energisation of the motor field.

In order to ensure smooth axial movement of the armature a brass orother non-magnetic sleeve can be provided which is secured to andconcentric with the armature and which slidingly engages the'innersurface of the poles. However, it will be appreciated that in theorysince the two poles will carry substantially identical pole shoes, theneven though asymmetric pole shoes may be used there will be no tendencyfor the armature to tilt relative to the' shaft 12 since equivalentsteps in the two pole shoes will be diametrically opposite one another,and so the force acting at any point on the armature will be balanced bythe same force at the diametrically opposite point on the armature.

In practice the armature, described above as being in the form ofa thickdisc,will include a peripheral flange at its axial end remote from thepoles, the flange engaging the poles in the full engagement position ofthe pinion assembly to limit the movement of the armature. A brass orother non-magnetic spacer can be secured to the flange to prevent theflange touching the poles and thereby facilitate return movement of thepinion and armature assembly upon de-energization of the winding 20.Moreover the poles described above as being formed in two separate partscan of course each be produced as a single part and furthermore in somestarter motors more than two equi-angularly spaced poles can beutilized. It is to be appreciated that where the required radial depthof the shaping of the pole is greater than the radial thickness of thepole shoe then the shaping, be it stepping or tapering, can be continuedon the pole body. Thus the shaping can be on part only of the radialthickness of the pole shoe, can be over the whole radial thickness ofthe pole shoe or can be over the whole radial thickness of the pole shoeand also on the pole body.

I claim:

l. A starter motor, for an internal combustion engine, comprising anelectric motor, a shaft rotatable by said motorand carrying a piniongear wheel, the pinion gear wheel being rotatable with said shaft andbeing movable axially relative to the shaft between a rest position andan operative position, and an electromagnet including an armaturecoupled to the pinion gear wheel said armature and said pinion gearwheel being movable axially relative to said shaft, a plurality ofelectro-' magnetic poles equi-angularly spaced around the axis of saidshaft in a plane at right angles to said axis and spaced apart by anamount such that the armature can enter between the poles, the polesbeing spaced from the armature, in the rest position thereof, in thedirection of movement of the armature relative to the shaft, each polebeing shaped so that the surface of each pole presented to the armaturein the rest position of the armature includes regions spaced from thearmature by different distances in the direction of movement and thearmature, and equally spaced from said shaft in a radial direction, amember magnetically interconnecting the poles, and an electromagnetwinding associated with the poles so that when energised the windinginduces a flow of magnetic flux between the poles and the armature,within the armature at right angles to its direction of movement, andbetween the poles, by way of said member, so that the armature isattracted to the poles, the arrrangement of said regions of the polesurfaces being chosen to achieve a predetermined attraction between thepoles and the armature during the movement of the armature towards thepoles.

2. A starter motor as claimed in claim 1 wherein said regions spacedfrom the armature by different distances in the direction of movement ofthe armature are defined by individual steps in said surface of thepole. I

3. A starter motor as claimed in claim 1 wherein said surface of eachpole tapers linearly in a direction away 4. A starter motor as claimedin claim 1 wherein said surface of each pole is curved, and said regionsspaced from the armature by different distances in the direction ofmovement of the armature are defined by areas from said armature, andsaid regions are constituted by 5 of said curved surface.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIUNPATENT NO. 1 3,848,148

DATED November 12, 1974 INVENTOR(S) 2 Ronald Wilson It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the Specification, column 3, line 33, cancel "0.15", insert 0.275line 34, cancel "0.275", insert 0.15 Cancel 0.00, insert 0.35 line 35,cancel "0.35", insert 0.00

Bigncd and gcaled this Third Day Of July 1979 [SEAL] Arrest:

LUTRELLE F. PARKE};

Attesting Oflicer Acting Commissioui of Patents and Trademarks UNITEDSTATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,848,148 DATED November 12, 1974 INVENTOR(S) Ronald Wilson It iscertified that error appears in the ab0ve-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the Specification, column 3, line 33, cancel 0.15", insert 0.275 line34, cancel "0.275", insert 0.15 Cancel 0.00", insert 0.35 line 35,cancel "0.35", insert 0.00

Signed and Scaled this Third Day of July 1979 [SEAL] Arrest.-

LUTRELLE F. PARKER Attestl'ng Oflicer Acting Commissioner ofPatents an;Trademarks

1. A starter motor, for an internal combustion engine, comprising anelectric motor, a shaft rotatable by said motor and carrying a piniongear wheel, the pinion gear wheel being rotatable with said shaft andbeing movable axially relative to the shaft between a rest position andan operative position, and an electromagnet including an armaturecoupled to the pinion gear wheel said armature and said pinion gearwheel being movable axially relative to said shaft, a plurality ofelectromagnetic poles equi-angularly spaced around the axis of saidshaft in a plane at right angles to said axis and spaced apart by anamount such that the armature can enter between the poles, the polesbeing spaced from the armature, in the rest position thereof, in thedirection of movement of the armature relative to the shaft, each polebeing shaped so that the surface of each pole presented to the armaturein the rest position of the armature includes regions spaced from thearmature by different distances in the direction of movement and thearmature, and equally spaced from said shaft in a radial direction, amember magnetically interconnecting the poles, and an electromagnetwinding associated with the poles so that when energised the windinginduces a flow of magnetic flux between the poles and the armature,within the armature at right angles to its direction of movement, andbetween the poles, by way of said member, so that the armature isattracted to the poles, the arrrangement of said regions of the polesurfaces being chosen to achievE a predetermined attraction between thepoles and the armature during the movement of the armature towards thepoles.
 2. A starter motor as claimed in claim 1 wherein said regionsspaced from the armature by different distances in the direction ofmovement of the armature are defined by individual steps in said surfaceof the pole.
 3. A starter motor as claimed in claim 1 wherein saidsurface of each pole tapers linearly in a direction away from saidarmature, and said regions are constituted by areas of the taperingsurface.
 4. A starter motor as claimed in claim 1 wherein said surfaceof each pole is curved, and said regions spaced from the armature bydifferent distances in the direction of movement of the armature aredefined by areas of said curved surface.